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3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Soil Organic Matter (Chapter 12) Notes
Soil Organic Matter (Chapter 12) Notes
Did you know .... Did you know that by composting you can create your own soil organic matter? Chapter 12 highlights soil organic matter and role in the global carbon cycle, creation of soil organic matter via decomposition, factors influencing soil organic matter production, and finally soil's role in the greenhouse gas effect.
Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil Organic Matter (Chapter 12) Videos A though F). Print or download lecture notes then view videos in succession alongside lecture content and add additional notes from each video. The start of each video is noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains lecture content through the note for the next video (e.g. Content for Video B).
Figures and tables unless specifically referenced are from the course text, Nature and Property of Soils, 14th Edition, Brady and Weil.
Content Video A
Soil Organic Matter (SOM)
AGRI1050R50: Introduction to Soil Science (2020S) LH
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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http://photogallery.nrcs.usda.gov/res/sites/photogallery/
Global Carbon Cycle
World Soil Carbon
Composition of Plants
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403415/View 3/11
Rates of Decomposition Sugars, Starches, Simple Proteins (Rapid Decomposition)
Crude Protein
Hemicellulose
Cellulose
Fats and Waxes
Lignins and Phenollics (Very Slow Decomposition)
Content Video B
Decomposition Breakdown of larger particles into smaller ones
Microbial Community – Work Force
Oxidation via Enzymes: Energy, CO2 gas, and H20
Enzymes – Catalyst – Easier/Faster
TONS of microbial enzymes
Important too for soil structure
Disassembly Plant – Aerobic and Anaerobic
Aerobic: CO2, NH4+, NO3-, HPO4-, SO4-, H2O
Microbial Biomass
Recalcitrant materials –Humus –SOM
Content Video C
Rates of Decomposition Physical
Smaller particles – Faster Degradation
Closer material is to microbes – Faster Degradation
Nutritional
Need balance
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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C:N Ratio – Ratio of Carbon to Nitrogen
C:N Ratio < 20 – Rapid Degradation, Mineralization
C:N Ration > 30 – Slow Degradation, Scavenge Nitrogen
Make additional N: Plant Available
C:N Ratios and Litter Quality Typical C:N Ratios
Litter Quality
Lignin Content
Low C:N: Low Lignin - High Quality, Faster nutrient availability, Less accumulation of SOM
High C:N: High Lignin – Lower quality, Slower release of nutrients, Accumulation of SOM
Manage residues and anticipate nutrient availabilities
Cover Crop Residue Decomposition
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Content Video D
Generating SOM SOM – Broad term
Living Biomass: Bugs and Animals
Plant Litter: Dead roots, identifiable residue
Humus: Soil colloid, High MW, unidentifiable reside
Soil Organic Carbon - % of Carbon in SOM
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Classifying SOM
Humus Humic Substances
Polymerization of lignin and degradation products
COMPLEX Ring Structures and Ill-defined
High MW
Recalcitrant – Resist microbial attack
Dark in Color
60-80% of SOM
Nonhumic Substances
20-30% of SOM
Less recalcitrant, Less Complex
Biomolecules – Microbial Byproducts
Polysaccharides
Impact soil structure – aggregate stability and nutrient availability
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Humus Influence Colloid
High Surface Area
High Water Holding Capacity
HIGH CEC: 150 to 500 cmolc/kg
Bank for nutrients
Promotes soil structure: air/gas exchange, infiltration rates, ETC.
Stable
Portions of SOM are very stable – Centuries old
Clay-Humus combination – further protection and stabilization
Continual, Slow Degradation: Must protect have and continually add residue to build new to replace loss
SOM Pools – Monitor and Predict
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Content Video E
Factors Influencing SOM Soil Orders
Alfisols – Lowest
Histosols – Highest
Texture
Clays > Sands
Complexation > Fine vs Coarse
Drainage Rates > Fine vs Coarse
Plant Cover
Plants > Bare
Grasslands > Forrest
Climate
Wet, Cold > Hot, Dry
Histosols: Waterlogged
Management – DO NOT DISTURB!
Distribution of SOM
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Managing Agronomic Soils – Building SOM Conservation and No-Till
Tillage: SOM broken down by microbial community
Crop Rotation
Crop Rotation > Monoculture
Maintain Soil pH and Nutrients
Nutrient availability for plants
Good for microbial population
Maximize CEC and Complexation for SOM
Plant Residues - Keep soil covered!
Crop Residues
Green Manures
Animal Manures
Morrow and Rothamstead Plots
Farmer's Challenge Aren’t bugs the bad guy here – Break down SOM?
Microbial community drive ALL nutrient cycling
SOM: CEC, WHC, Nutrient Availability, Structure
BALANCE
Content Video F
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403415/View 10/11
Content Video F
Composting Create own humus!
Produce soil amendment from decomposition of organic materials
Management of compost pile – Box 12.4
Composting – animal manure - minimize pathogens
Soils and Greenhouse Effect Soils natural source GHG: CO2,CH4, NOx Loss of SOM – Net Loss CO2 Manage Soils SINK most gases:
Stop draining Histosols Manage wet soils Manage for increased SOM
Carbon Credit Industry
Review What part does soil play in the global carbon cycle? Where is most of the carbon in soils located? What is the primary source for the production of SOM? Are soil nutrients a large portion of the total plant material? Do all plant materials decay at the same rate? What is decomposition? What group drives decomposition? What is an enzyme? Which is more efficient aerobic or anaerobic degradation? Why is the nutrient content of plant material so important in is degradation status? What is a C:N ratio – why is it important – what C:N ratio would cause mineralization and not immobilization? What is litter quality? What qualities of litter promote SOM? Can you describe Figure 12.6? Name the major components of SOM? Of 100 grams of carbon the majority is lost to what? What are some characteristics of humus? Why is SOM so closely tied to soil fertility? Understand the pools of SOM – active vs passive What soil orders might have the highest and lowest SOM? Generally would clay soils or sandy soils tend to have greater amounts of OM and WHY? What climactic conditions are most conductive to maximum SOM? D d t d Fi 12 21?
3/19/2020 Soil Organic Matter (Chapter 12) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403415/View 11/11
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Do you understand Figure 12 21?
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